Successful attempts to understand the physiological mechanisms of vision have already had, and will continue to have, general applications to the management of ocular dysfunction. More specifically, those studies that further our understanding of the kinds of signal-processing that occur in the retina itself may contribute not only to the diagnosis and treatment of retinal diseases, but also to the eventual development of prosthetic replacements for loss of retinal function. The studies described here are of this type. We propose to measure the spatial charateristics of local retinal adaption by studies of rhe post-receptor afterimage. Preliminary to the main set of experiments, we will determine the effects of the surround (stabilized and unstabilized) and stimulus area on the form and magnitude of the stabilized MTF. Then we will measure the spatial charaecteristics of local adaptation by measuring the contrast of a test grating required to cancel the afterimage of since-wave adapting gratings of farious contrasts. As a check on the linearity of the process and as a back-up procedure, we also propose to measure increment thresholds on the afterimage of a step function. From these two sets of experiments, we will determine the contrast-reducing effects of local adaptation on stabilized, stationary gratings. These effects will be factored out of the stabilized MTF to infer the sensitivity of the rest of the visual system to temporally unmodulated stimuli. Similar experiments and calculations of the effects of local adaptation will be done with slowlly drifting gratings. These local-adaptation-free spatial MTFs will be compared to determine the temporal tuning of the visual system at very slow temporal modulations. Finally, we will explore other characteristics of the residual sensitivity to stabilized images, under the hypothesis that it is resonsible in part of their periodic reappearance.